Note: This post talks about official forecasts for this winter and is the final part of my series on my thoughts for the upcoming winter. Other posts in this series can be found here.
HOW THE FORECAST WORKS
Before we look at long-range forecasts from the Climate Prediction Center (CPC) and Environment Canada, it is important to understand what these forecasts represent, and (more importantly) what they don’t represent. Like I said in the first part of this series, long-range forecasts are very generalized, both with respect to geography and time. To get a better idea of this, we’ll take the forecast issued by the CPC for the month of November.
The two types of outlooks we will be looking at are for temperature and precipitation. In both of these, there are only three categories considered in the forecast: above-average temperature/precipitation, near-average, and below-average. These are depicted on the map using the following colors:
| Temperature | Precipitation | |
| Above-average | Orange/red | Yellow/brown |
| Near-average | Gray | Gray |
| Below-average | Blue | Green |
Deeper colors on the map represent a higher chance of a particular condition. In the example above, the red covering parts California, Nevada, and Arizona is the highest chance (60%) of above-average temperatures for November. The brown located over northern Utah represents the highest chance (50%) of below-average precipitation for November. It would be easy to assume that darker colors would be more extreme (like perhaps California being higher above average than Washington), but this is not the case.
While a higher chance can often imply more extreme conditions because that often shows up on weather models better, this map is only concerned with chances. The last color to discuss is white. Areas in the United States on the map that are white are areas where there are equal chances of the three categories occurring, so a 33% chance of above-average conditions, 33% for near-average, and 33% for below-average.
Let’s continue with temperatures in the Southwest as our example from above. This outlook is not saying that the Southwest will spend the entire month warmer than average, but that when we take an average of temperatures through the month (the average mean) of November there is a 60% chance that that number will come out above-average. In Reno, the average mean temperature for November 1-14 is 45.6°, but the average mean for that same period in 2019 comes out to 51.0°. This puts Reno very definitively above-average thus far, meaning that the forecast so far has been accurate. While most days so far this month have been warmer than average, the 1st was actually below-average.
Time will tell if the rest of the month will come out to above average for Reno, but the important point to take from this is that when above-average temperatures are mentioned in these outlooks, below-average days can (and likely will) still happen. The forecast is judged to have been correct or incorrect based on the average mean temperature or total precipitation for the time period, not specific conditions on individual days.
CLIMATE PREDICTION CENTER OUTLOOK
Now that I’ve tried my best to explain how the outlook works, let’s take a look at what the Climate Prediction Center has for us this winter. A word of caution – it’s important to not try to read too much into these outlooks.
The first thing that pops out to me is on the precipitation map. The white area covering Washington and Oregon displays equal chances (near 33%) of all three precipitation categories. There’s not really much to glean from this. We just simply don’t have a clear idea of what to expect in our region.
The temperature outlook is interesting, though. The current outlook leans toward an above-average winter for the Columbia Basin, but it’s important to note that this forecast does not display a large amount of confidence for anywhere except western and northern Alaska.
The National Weather Service also provides a tool where we can look at specific percent chances for specified points around the nation. When we look at the specific numbers for the Tri-Cities (above on mobile, on the right on larger screens), we see that there is only a 38% chance of above-average temperatures. This is accompanied by a 34% chance of near-average temperatures.
Like I said above, the outlook leans toward above-average for temperature for December through February, but not by much. It does seem quite unlikely that we will see overall winter temperatures come out to be below-average, but just as in the example of Reno, this does not mean that we won’t have any days below average.
ENVIRONMENT CANADA OUTLOOK
I’m not going to spend much time discussing the forecast issued by the Climate Prediction Center’s Canadian counterparts, but I think it is helpful to get a second opinion. The Canadian outlook does not cover the Columbia Basin, but it does cover the western side of the state as well as eastern Washington approximately north of I-90.
Looking at the parts of Washington and Idaho that are included on the map, as well as southern British Columbia, show that the forecasts are generally similar to those from the Climate Prediction Center. There are a few small discrepancies in exact percentages, which is to be expected from different groups of forecasters. The Canadian group seems to have slightly higher chances of above-average temperatures and above-average precipitation.
We can determine just how different the forecasts are when we look at chances for Spokane, which are just about the same as for the Tri-Cities. With that information, it appears that the difference in the forecasts from the two groups is only between 2% and 10%. While there are probably subtle and very specialized differences, for the purposes of this series I would say the two are close enough to imply similar conditions.
TEMPERATURE INVERSIONS
One thing to keep in mind with periods of above-average temperatures is that regional temperatures can be quite warm while we remain pretty cold here in the Columbia Basin. This is thanks to the temperature inversions we get in the winter. When an area of strong high pressure is positioned over the Pacific Northwest for several days, it mashes everything it can down into valleys and basins – like the one we call home.
Because the sun is so low on the horizon this time of year, it doesn’t warm the ground as effectively. Cooler ground temperatures mean that the air doesn’t get as warm, making it so that the cold air that sinks to the bottom of the basin remains trapped there, rather than moving around and mixing with warmer air above.
The lack of mixing causes pollutants to build up in the basin, lowering our air quality. It also helps to hold in moisture, which can develop into low clouds and fog. When these form, it keeps our temperatures even cooler because the ground gets warmed even less by the sun. I discussed specific examples of regional temperatures during inversion events in the part of this series where I discussed analog years.
CONCLUSION
While I did not give my own personal forecast for this winter, I hope you enjoyed my discussions on the El Niño-Southern Oscillation, the Blob, several past years, and government forecasts. Seasonal forecasting is a very complex scientific endeavor that requires intimate knowledge of a number of global meteorological and oceanographic phenomenon. My goal with this series was to help provide an idea of the range of possibilities that are possible as we progress into winter.
Regardless of what happens, you’ll be able to get up to date forecasts and information over on my Facebook page – Tri-Cities Weather. Thank you for reading!
